To induce antigen-specific T cell activation and clonal expansion, two signals provided by antigen-presenting cells (APCs) must be delivered to the surface of resting T lymphocytes (Jenkins, M. and Schwartz, R. (1987) J. Exp. Med. 165, 302-319; Mueller, D. L., et al. (1990) J. Immunol. 144, 3701-3709; Williams, I. R. and Unanue, E. R. (1990) J. Immunol. 145, 85-93). The first signal, which confers specificity to the immune response, is mediated via the T cell receptor (TCR) following recognition of foreign antigenic peptide presented in the context of the major histocompatibility complex (MHC). The second signal, termed costimulation, induces T cells to proliferate and become functional (Schwartz, R. H. (1990) Science 248, 1349-1356). Costimulation is neither antigen-specific, nor MHC restricted and is thought to be provided by one or more distinct cell surface molecules expressed by APCs (Jenkins, M. K., et al. (1988) J. Immunol. 140, 3324-3330; Linsley, P. S., et al. (1991) J. Exp. Med. 173, 721-730; Gimmi, C. D., et al., (1991) Proc. Natl. Acad. Sci. USA. 88, 6575-6579; Young, J. W., et al. (1992) J. Clin. Invest. 90, 229-237; Koulova, L., et al. (1991) J. Exp. Med. 173, 759-762; Reiser, H., et al. (1992) Proc. Natl. Acad Sci. USA. 89, 271-275; van-Seventer, G. A., et al. (1990) J. Immunol. 144, 4579-4586; LaSalle, J. M., et al., (1991) J. Immunol. 147, 774-80; Dustin, M. I., et al., (1989) J. Exp. Med. 169, 503; Armitage, R. J., et al. (1992) Nature 357, 80-82; Liu, Y., et al. (1992) J. Exp. Med. 175, 437-445).
Considerable evidence suggests that the B7 protein, expressed on APCs, is one such critical costimulatory molecule (Linsley, P. S., et al., (1991) J. Exp. Med. 173, 721-730; Gimmi, C. D., et al., (1991) Proc. Natl. Acad. Sci. USA. 88, 6575-6579; Koulova, L., et al., (1991) J. Exp. Med 173, 759-762; Reiser, H;, et al. (1992) Proc. Natl. Acad Sci. USA. 89, 271-275; Linsley, P. S. et al. (1990) Proc. Natl. Acad. Sci. USA. 87, 5031-5035; Freeman, G. J. et al. (1991) J. Exp. Med. 174,625-631.). B7 is the counter-receptor for two ligands expressed on T lymphocytes. The first ligand, termed CD28, is constitutively expressed on resting T cells and increases after activation. After signaling through the T cell receptor, ligation of CD28 induces T cells to proliferate and secrete IL-2 (Linsley, P. S., et al. (1991) J. Exp. Med. 173, 721-730; Gimmi, C. D., et al. (1991) Proc. Natl Acad. Sci. USA. 88, 6575-6579; Thompson, C. B., et al. (1989) Proc. Natl. Acad. Sci. USA. 86, 1333-1337; June, C. H., et al. (1990) Immunol. Today. 11, 211-6; Harding, F. A., et al. (1992) Nature. 356, 607-609.). The second ligand, termed CTLA4 is homologous to CD28 but is not expressed on resting T cells and appears following T cell activation (Brunet, J. F., et al., (1987) Nature 328, 267-15 270). DNA sequences encoding the human and murine CTLA4 protein are described in Dariavach, et al. (1988) Eur. J. Immunol. 18(12), 1901-1905; Brunet, J. F., et al. (1987) supra; Brunet, J. F. et al. (1988) Immunol. Rev. 103:21-36; and Freeman, G. J., et al. (1992) J. Immunol. 149, 3795-3801. Although B7 has a higher affinity for CTLA4 than for CD28 (Linsley, P. S., et al., (1991) J. Exp. Med. 174, 561-569), the function of CTLA4 is still unknown.
The importance of the B7:CD28/CTLA4 costimulatory pathway has been demonstrated in vitro and in several in vivo model systems. Blockade of this costimulatory pathway results in the development of antigen specific tolerance in murine and humans systems (Harding, F. A., et al. (1992) Nature. 356, 607-609; Lenschow, D. J., et al. (1992) Science. 257, 789-792; Turka, L. A., et al. (1992) Proc. Natl. Acad. Sci. USA. 89, 11102-11105; Gimmi, C. D., et al. (1993) Proc. Natl. Acad. Sci USA 90, 6586-6590; Boussiotis, V., et al. (1993) J. Exp. Med. 178, 1753-1763). Conversely, expression of B7 by B7 negative murine tumor cells induces T-cell mediated specific immunity accompanied by tumor rejection and long lasting protection to tumor challenge (Chen, L., et al. (1992) Cell 71, 1093-1102; Townsend, S. E. and Allison, J. P. (1993) Science 259, 368-370; Baskar, S., et al. (1993) Proc. Natl. Acad. Sci. 90, 5687-5690.). Therefore, manipulation of the B7:CD28/CTLA4 pathway offers great potential to stimulate or suppress immune responses in humans.
This invention pertains to isolated nucleic acids encoding novel molecules which costimulate T cell activation. Preferred costimulatory molecules include antigens on the surface of B lymphocytes, professional antigen presenting cells (e.g., monocytes, dendritic cells, Langerhan cells) and other cells (e.g., keratinocytes, endothelial cells, astrocytes, fibroblasts, oligodendrocytes) which present antigen to immune cells, and which bind either CTLA4, CD28, both CTLA4 and CD28 or other known or as yet undefined receptors on immune cells. Such costimulatory molecules are referred to herein as CTLA4/CD28 binding counter-receptors or B lymphocyte antigens, and are capable of providing costimulation to activated T cells to thereby induce T cell proliferation and/or cytokine secretion. Preferred B lymphocyte antigens include B7-2 and B7-3 and soluble fragments or derivatives thereof which bind CTLA4 and/or CD28 and have the ability to inhibit or induce costimulation of immune cells. In one embodiment, an isolated nucleic acid which encodes a peptide having the activity of the human B7-2 B lymphocyte antigen is provided. Preferably, the nucleic acid is a cDNA molecule having a nucleotide sequence encoding human B7-2, as shown in FIG. 8 (SEQ ID. NO:1). In another embodiment, the nucleic acid is a cDNA molecule having a nucleotide sequence encoding murine B7-2, as shown in FIG. 14 (SEQ ID NO:22).
The invention also features nucleic acids which encode a peptide having B7-2 activity and at least about 50%, more preferably at least about 60% and most preferably at least about 70% homologous with an amino acid sequence shown in FIG. 8 (SEQ ID NO:2) or an amino acid sequence shown in FIG. 14 (SEQ ID NO:23). Nucleic acids which encode peptides having B7-2 activity and at least about 80%, more preferably at least about 90%, more preferably at least about 95% and most preferably at least about 98% or at least about 99% homologous with an amino acid sequence shown in FIG. 8 (SEQ ID NO:2) or an amino acid sequence shown in FIG. 14 (SEQ ID NO:23) are also within the scope of the invention. In another embodiment, the peptide having B7-2 activity is encoded by a nucleic acid which hybridizes under high or low stringency conditions to a nucleic acid which encodes a peptide having an amino acid sequence of FIG. 8 (SEQ ID NO:2) or a peptide having an amino acid sequence shown in FIG. 14 (SEQ ID NO:23).
The invention further pertains to an isolated nucleic acid comprising a nucleotide sequence encoding a peptide having B7-2 activity and having a length of at least 20 amino acid residues. Peptides having B7-2 activity and consisting of at least 40 amino acid residues in length, at least 60 amino acid residues in length, at least 80 amino acid residues in length, at least 100 amino acid residues in length or at least 200 or more amino acid residues in length are also within the scope of this invention. Particularly preferred nucleic acids encode a peptide having B7-2 activity, a length of at least 20 amino acid residues or more and at least 50% or greater homology (preferably at least 70%) with a sequence shown in FIG. 8 (SEQ ID NO:2).
In one preferred embodiment, the invention features an isolated DNA encoding a peptide having B7-2 activity and an amino acid sequence represented by a formula:
Xn-Y-Zm
In the formula, Y consists essentially of amino acid residues 24-245 of the sequence shown in FIG. 8 (SEQ ID NO:2). Xn and Zm are additional amino acid residue(s) linked to Y by an amide bond. Xn and Zm are amino acid residues selected from amino acid residues contiguous to Y in the amino acid sequence shown in FIG. 8 (SEQ ID NO:2). Xn is amino acid residue(s) selected from amino acids contiguous to the amino terminus of Y in the sequence shown in FIG. 8 (SEQ ID NO:2), i.e., selected from amino acid residue 23 to 1. Zm is amino acid residue(s) selected from amino acids contiguous to the carboxy terminus of Y in the sequence shown in FIG. 8 (SEQ ID NO:2), i.e., selected from amino acid residue 246 to 329. According to the formula, n is a number from 0 to 23 (n=0-23) and m is a number from 0 to 84 (m=0-84). A particularly preferred DNA encodes a peptide having an amino acid sequence represented by the formula Xn-Y-Zm, where Y is amino acid residues 24-245 of the sequence shown in FIG. 8 (SEQ ID NO:2) and n=0 and m=0.
The invention also features an isolated DNA encoding a B7-2 fusion protein which includes a nucleotide sequence encoding a first peptide having B7-2 activity and a nucleotide sequence encoding a second peptide corresponding to a moiety that alters the solubility, binding affinity, stability or valency of the first peptide. Preferably, the first peptide having B7-2 activity includes an extracellular domain portion of the B7-2 protein (e.g., about amino acid residues 24-245 of the sequence shown in FIG. 8 (SEQ ID NO:2)) and the second peptide is an immunoglobulin constant region, for example, a human Cxcex31 or Cxcex34 domain, including the hinge,; CH2 and CH3 region, to produce a B7-2 immunoglobulin fusion protein (B7-2Ig)(see Capon et al. (1989) Nature 337, 525-531 and Capon U.S. Pat. No. 5,116,964).
The nucleic acids obtained in accordance;with the present invention can be inserted into various expression vectors, which in turn direct the synthesis of the corresponding protein or peptides in a variety of hosts, particularly eucaryotic cells, such as mammalian and insect cell culture, and procaryotic cells such as E. coli. Expression vectors within the scope of the invention comprise a nucleic acid encoding at least one peptide having the activity of a novel B lymphocyte antigen as described herein, and a promoter operably linked to the nucleic acid sequence. In one embodiment, the expression vector contains a DNA encoding a peptide having the activity of the B7-2 antigen and a DNA encoding a peptide having the activity of another B lymphocyte antigen, such as the previously characterized B7 activation antigen, referred to herein as B7-1. Such expression vectors can be used to transfect host cells to thereby produce proteins and peptides, including fusion proteins, encoded by nucleic acids as described herein.
Nucleic acid probes useful for assaying a biological sample for the presence of B cells expressing the B lymphocyte antigens B7-2 and B7-3 are also within the scope of the invention.
The invention further pertains to isolated peptides having the activity of a novel B lymphocyte antigen, including the B7-2 and B7-3 protein antigens. A preferred peptide having B7-2 activity is produced by recombinant expression and comprises an amino acid sequence shown in FIG. 8 (SEQ ID NO: 2). Another preferred peptide having B7-2 activity comprises an amino acid sequence shown in FIG. 14 (SEQ ID NO:23). A particularly preferred peptide having the activity of the B7-2antigen includes at least a portion of the mature form of the protein, such as an extracellular domain portion (e.g., about amino acid residues 24-245 of SEQ ID NO:2) which can be used to enhance or suppress T-cell mediated immune responses in a subject. Other preferred peptides having B7-2 activity include peptides having an amino acid sequence represented by a formula:
Xn-Y-Zm
In the formula, Y is amino acid residues selected from the group consisting of: amino acid residues 55-68 of the sequence shown in FIG. 8 (SEQ ID NO:2); amino acid residues 81-89 of the sequence shown in FIG. 8 (SEQ ID NO:2); amino acid residues 128-142 of the sequence shown in FIG. 8 (SEQ ID NO:2); amino acid residues 160-169 of the sequence shown in FIG. 8 (SEQ ID NO:2); amino acid residues 188-200 of the sequence shown in FIG. 8 (SEQ ID NO:2); and amino acid residues 269-282 of the sequence shown in FIG. 8 (SEQ ID NO:2). In the formula Xn and Zm are additional amino acid residue(s) linked to Y by an amide bond and are selected from amino acid residues contiguous to Y in the amino acid sequence shown in FIG. 8 (SEQ ID NO:2). Xn is amino acid residue(s) selected from amino acids contiguous to the amino terminus of Y in the sequence shown in FIG. 8 (SEQ ID NO:2). Zm is amino acid residue(s) selected from amino acids contiguous to the carboxy terminus of Y in the sequence shown in FIG. 8 (SEQ ID NO:2). According to the formula, n is a number from 0 to 30 (n=0-30) and m is a number from 0 to 30 (m=0-30).
Fusion proteins or hybrid fusion proteins including a peptide having the activity of a novel B lymphocyte antigen (e.g., B7-2, B7-3) are also featured. For example, a fusion protein comprising a first peptide which includes an extracellular domain portion of a novel B lymphocyte antigen fused to second peptide, such as an immunoglobulin constant region, that alters the solubility, binding affinity, stability and/or valency of the first peptide are provided. In one embodiment, a fusion protein is produced comprising a first peptide which includes amino acid residues of an extracellular domain portion of the B7-2 protein joined to a second peptide which includes amino acid residues of a sequence corresponding to the hinge, CH2 and CH3 regions of Cxcex31 or Cxcex34 to form a B7-2Ig fusion protein. In another embodiment, a hybrid fusion protein is produced comprising a first peptide which includes an extracellular domain portion of the B7-1 antigen and an extracellular domain portion of the B7-2 antigen and a second peptide which includes amino acid residues corresponding to the hinge, CH2 and CH3 of Cxcex31 (see e.g., Linsley et al. (1991) J. Exp. Med. 1783:721-730; Capon et al. (1989) Nature 337, 525-531; and Capon U.S. Pat. No. 5,116,964). In a yet another embodiment, a hybrid fusion protein comprises the immunoglobulin-like variable domain of B7-2, but not the immunoglobulin-like constant domain of B7-2, linked to the constant region of an immunoglobulin molecule. In a preferred embodiment, the B7-2Ig fusion protein includes the variable domain of human B7-2, preferably from about amino acid residue 24 to about amino acid residue 133 of the human B7-2 protein (as shown SEQ ID NO: 2), fused to the constant region of an IgG molecule.
Isolated peptides and fusion proteins of the invention can be administered to a subject to either upregulate or inhibit the expression of one or more B lymphocyte antigens or block the ligation of one or more B lymphocyte antigens to their natural ligand on immune cells, such as T cells, to thereby provide enhancement or suppression of cell-mediated immune responses in vivo.
Another embodiment of the invention provides antibodies, preferably monoclonal antibodies, specifically reactive with a peptide of a novel B lymphocyte antigen or fusion protein as described herein. Preferred antibodies are anti-human B7-2 monoclonal antibodies produced by hybridoma cells HF2.3D1, HA5.2B7 and HA3.1F9. These hybridoma cells have been deposited with the American Type Culture Collection at ATCC Accession No. HB11686 (HF2.3D1), ATCC Accession No. HB 11687 (HA5.2B7), and ATCC Accession No. HB11688 (HA3.1F9).
A still further aspect of the invention involves the use of the nucleic acids of the invention, especially the cDNAs, to enhance the immunogenicity of a mammalian cell. In preferred embodiments, the mammalian cell is a tumor cell, such as a sarcoma, a lymphoma, a melanoma, a neuroblastoma, a leukemia or a carcinoma, or an antigen presenting cell, such as a macrophage, which is transfected to allow expression of a peptide having the activity of a novel B lymphocyte antigen of the invention on the surface of the cell. Macrophages that express a peptide having the activity of a B lymphocyte antigen, such as the B7-2 antigen, can be used as antigen presenting cells, which, when pulsed with an appropriate pathogen-related antigen or tumor antigen, enhance T cell activation and immune stimulation.
Mammalian cells can be transfected with a suitable expression vector containing a nucleic acid encoding a peptide having the activity of a novel B lymphocyte antigen, such as the B7-2 antigen, ex vivo and then introduced into the host mammal, or alternatively, cells can be transfected with the gene in vivo via gene therapy techniques. For example, the nucleic acid encoding a peptide having B7-2 activity can be transfected alone, or in combination with nucleic acids encoding other costimulatory molecules. In enhancing the immunogenicity of tumors which do not express Class I or Class II MHC molecules, it may be beneficial to additionally transfect appropriate class I or II genes into the mammalian cells to be transfected with a nucleic acid encoding a peptide having the activity of a B lymphocyte antigen, as described herein.
The invention also provides methods for inducing both general immunosuppression and antigen-specific tolerance in a subject by, for example, blocking the functional interaction of the novel B lymphocyte antigens of the invention, e.g., B7-2 and B7-3, to their natural ligand(s) on T cells or other immune system cells, to thereby block co-stimulation through the receptor-ligand pair. In one embodiment, inhibitory molecules that can be used to block the interaction of the natural human B7-2 antigen to its natural ligands (e.g., CTLA4 and CD28) include a soluble peptide having B7-2 binding activity but lacking the ability to costimulate immune cells, antibodies that block the binding of B7-2 to its ligands and fail to deliver a co-stimulatory signal (so called xe2x80x9cblocking antibodiesxe2x80x9d, such as blocking anti-B7-2 antibodies), B7-2-Ig fusion proteins, which can be produced in accordance with the teachings of the present invention, as well as soluble forms of B7-2 receptors, such as CTLA4Ig or CD28Ig. Such blocking agents can be used alone or in combination with agents which block interaction of other costimulatory molecules with their natural ligands (e.g., anti-B7 antibody). Inhibition of T-cell responses and induction of T cell tolerance according to the methods described herein may be useful prophylactically, in preventing transplantation rejection (solid organ, skin and bone marrow) and graft versus host disease, especially in allogeneic bone marrow transplantation. The methods of the invention may also be useful therapeutically, in the treatment of autoimmune diseases, allergy and allergic reactions, transplantation rejection, and established graft versus host disease in a subject.
Another aspect of the invention features methods for upregulating immune responses by delivery of a costimulatory signal to T cells through use of a stimulatory form of B7-2 antigen, which include soluble, multivalent forms of B7-2 protein,-such as a peptide having B7-2 activity and B7-2 fusion proteins. Delivery of a stimulatory form of B7-2 in conjunction with antigen may be useful prophylactically to enhance the efficacy of vaccination against a variety of pathogens and may also be useful therapeutically to upregulate an immune response against a particular pathogen during an infection or against a tumor in a tumor-bearing host.
The invention also features methods of identifying molecules which can inhibit either the interaction of B lymphocyte antigens, e.g., B7-2, B7-3, with their receptors or interfere with intracellular signalling through their receptors. Methods for identifying molecules which can modulate the expression of B lymphocyte antigens on cells are also provided. In addition, methods for identifying cytokines produced in response to costimulation of T cells by novel B lymphocyte antigens are within the scope of the invention.